This invention relates to a gable top type carton fashioned from a unitary blank of paperboard, the blank being provided with a thermoplastic coating or layer on both surfaces and also provided with a plurality of fold lines to facilitate its assembly or erection.
The prior art is aware of a variety of constructions of gable top type paperboard cartons. After filling with a beverage, the top of the carton is closed and sealed, often by the application of heat and pressure along what is termed a fin or rib running across the top of the carton. The paperboard being coated with a thermoplastic material, typically polyethylene, such application of heat and pressure fuses certain surface portions of the polyethylene on opposing roof panels and on opposing pour spout panels, to thereby effect a seal. However, such a procedure for sealing the carton has had the disadvantage that upon initial opening, the polyethylene coatings which are adhered to each other do not easily separate, with the result that either the carton partially rips the polyethylene or separates from the paperboard fibers causing an unslightly appearance and making it difficult to open for dispensing of the beverage carried by it.
To overcome the problem of difficulty of opening, workers in this art have used what is termed adhesives on certain portions of the gable top panels which abut each other in the seal area and tack together prior to carton opening. An adhesive is a substance which will reduce the bond strength of the opposing surfaces ability to stick together. Adhesives are usually coated on strategic areas of the polymer surface. This coating prevents the bonding action available from the fused thermoplastic. The result being enough adhesion between the polymer layers to maintain the carton in a closed condition, with the remaining abutting surfaces of the gable top being coated with adhesive to facilitate easier opening. The perimeter abutting the adhesive coating is not coated. A heat seal bond is achieved around this adhesive thus keeping the container closed during transit. An example of an adhesive construction is shown in U.S. Pat. Re. No. 26,305 issued to Huang et al. There, adhesive coatings are denoted by the numerals 83, 84, 85 and 86 of FIG. 1, as well as adhesive coatings 87 and 88 of FIG. 2. Another typical prior art construction employing adhesives is given in U.S. Pat. No. 4,775,096 issued to Andersson et al. In the Huang construction, the adhesive coatings are employed both on the interior surface of the pouring spout, as well as on the exterior surface (the latter coatings denoted by the numerals 87 and 88), while in the Andersson patent, adhesive coatings D and E are employed on the internal pour spout surfaces, as well as C and F on the roof fin seal panels.
While solving the problem of permitting ease of opening by the consumer of the carton without tearing of the paperboard, the use of abhesive coatings has a significant drawback in the packaging of liquids which are intended to be stored over extended periods of time. Such packages have been termed extended shelf life packages. The use of adhesives does not produce as complete as seal as is possible with an adhesive. Accordingly, up until the time of this invention, manufacturers of gable top paperboard cartons for beverages which are intended for long shelf life have not had available to them a carton construction which will permit easy initial opening of the carton. In addition, the use of adhesives for refrigerated products has long been practiced in the industry. This adhesive has caused problems in leakage if too much is used and, conversely, problems in opening when too little is used. The control of the adhesive material lay down is critical and difficult under normal production conditions.